Generally, to provide a broadcasting service, a main transmitter and a repeater are disposed depending on a peripheral topography and natural feature, and depending on a service area of a broadcasting company. The repeater is installed at an area where a weak broadcast signal is received from the main transmitter, and operates to strengthen the signal and to increase a signal transmission area from the main transmitter.
FIG. 1 is a view depicting an example of a broadcasting service using a conventional repeater, and illustrates each repeater using frequencies different from one another.
As shown in FIG. 1, in the broadcasting service using the conventional repeater, first, a main transmitter 101 transmits a broadcast signal using a transmission frequency (A), and each of repeaters 102 to 105 repeats a signal using a different frequency from the transmission frequency (A). However, since the conventional repeater of FIG. 1 assigns a different frequency to each of the repeaters 102 to 105 to solve the weak signal problem for the signal received from the main transmitter 101 or to increase the broadcast zone, the conventional repeater is inefficient in frequency utilization in that each of the repeaters 102 to 105 uses a plurality of frequency bands which in turn utilizes a large amount of frequency resources.
FIG. 2 is a view depicting another example of the broadcasting service using the conventional repeater, and illustrates a conceptual view of the broadcasting service in which the on-channel repeater repeats using the same frequency. In other words, a main transmitter 201 transmits a broadcast signal using a transmission frequency (A), and each of the on-channel repeaters 202 to 205 repeats the broadcast signal using the same frequency as the transmission frequency (A). In order to enable the broadcasting service, a receiver should be able to distinguish from one another the broadcast signals transmitted from the main transmitter 201 and the on-channel repeaters 202 to 205 using the same frequency band.
Generally, a receiver includes an equalizer to eliminate multipath signals and the equalizer also eliminates delayed input signals having an identical frequency.
However, if signals from the main transmitter 201 and the on-channel repeaters 202 to 205 using the same frequency bandwidth are not identical, the signals become noise signals relative to each other. These noise signals cannot be eliminated by the equalizer. Furthermore, if each of signals from the main transmitter 201 and the on-channel repeaters 202 to 205 is delayed as long as a predetermined time that could not be permitted to the equalizer, the equalizer could not eliminate the delayed signal.
Accordingly, in order to provide a digital broadcasting service using the on-channel repeater, it is required as a precondition that the output signal of the on-channel repeater should be the same as the output signal of the main transmitter, and time-delaying of the two output signals should be low.
The following explanation is provided to illustrate the drawbacks occurring when a signal is repeated using the conventional on-channel repeater with reference to FIGS. 3 to 6.
FIG. 3 is an exemplary view illustrating a construction of a conventional RF amplification on-channel repeater.
As shown in FIG. 3, in the conventional RF amplification on-channel repeater, a RF broadcast signal is received from a main transmitter through a reception antenna 301 and a RF receiving unit 302, the received RF signal passes through a RF band pass filter 303 only at a desired signal band, the band passed RF signal is amplified through a high power amplifying unit 304 and then transmitted through a transmission antenna 305 of the on-channel repeater over an on-channel. The RF amplification on-channel repeater has a characteristic of a low system delay and a simple structure.
FIG. 4 is an exemplary view illustrating a construction of a conventional IF conversion on-channel repeater.
As shown in FIG. 4, in the conventional IF conversion on-channel repeater, a RF broadcast signal is received from a main transmitter through a reception antenna 401 and a RF receiving unit 402. The received RF signal is converted into an IF signal through an IF down-converting unit 403, and the IF signal passes through the IF band pass filter 404 only at a desired signal band. The band passed IF signal is converted into a RF broadcast signal through the RF up-converting unit 405, and the RF broadcast signal is amplified through a high power amplifying unit 406 and then transmitted through a transmission antenna 407. The IF conversion on-channel repeater also has a low system delay and a simple structure. Further, a selection characteristic of the band pass filter is superior to that of the RF amplification on-channel repeater of FIG. 3.
FIG. 5 is an exemplary view illustrating a construction of a conventional Surface Acoustic Wave (SAW) filter on-channel repeater.
As shown in FIG. 5, in the conventional SAW filter on-channel repeater, a RF broadcast signal is received from a main transmitter through a reception antenna 501 and a RF receiving unit 502, and the received RF broadcast signal is converted into an IF signal through an IF down-converting unit 503. The IF signal passes through an SAW filter 504 only at a desired signal band, and the SAW filtered IF signal is converted into a RF broadcast signal through a RF up-converting unit 505. The RF broad signal is amplified through a high power amplifying unit 506 and then transmitted through a transmission antenna 507. The SAW filter on-channel repeater has also a low system delay and a simple structure. Further, a selection characteristic of the SAW filter is superior to that of the IF conversion on-channel repeater of FIG. 4.
FIG. 6 is an exemplary view illustrating a construction of a conventional demodulation/modulation on-channel repeater.
As shown in FIG. 6, in the conventional demodulation/modulation on-channel repeater, a RF broadcast signal is received from a main transmitter through a reception antenna 601 and a RF receiving unit 602. The received RF broadcast signal is converted into an IF signal through an IF down-converting unit 603. The IF signal is converted into a baseband signal through a demodulating unit 604. The noise and multi-path signals generated due to the transmission channel between the main transmitter and the on-channel repeater are removed from the converted baseband signal in an equalizer unit and forward error correction (FEC) decoding unit 605. The output signal of the equalizer unit and FEC decoding unit 605 is error-correction encoded through FEC encoding unit 606. The FEC-encoded signal is converted into an IF band broadcasting signal through a modulating unit 607. The converted IF signal is converted into a RF broadcast signal through a RF up-converting unit 608, and the RF broadcast signal is amplified through a high power amplifying unit 609 and then transmitted through a transmission antenna 610.
In the conventional on-channel repeater in FIGS. 3 to 6, the characteristics of the output signals of the on-channel repeaters are inferior to those of the input signals of the on-channel repeaters since the noise and multi-path signals generated due to the transmission channel between the main transmitter and the on-channel repeater, the feedback signal generated due to the low isolation of the transmission/reception antennas, and a system noise added from an on-channel repeater system, etc. cannot be removed. The above mentioned conventional on-channel repeaters shown in FIGS. 3 to 6 have drawbacks in that the transmission power of the on-channel repeater is limited due to the feedback signal generated due to the low isolation of the transmission/reception antennas.
The conventional on-channel repeater having a modulating unit and a demodulating unit in FIG. 6 improves a function of removing a noise on the conventional on-channel repeaters in FIGS. 3 to 5. However, since the conventional demodulation/modulation on-channel repeater in FIG. 6 includes a FEC decoding unit and a FEC encoding unit, the time delay in the on-channel repeater is increased from few microseconds to few milliseconds. Since the output signal generated due to ambiguity of a general standard trellis encoder of FIG. 6 is recognized as a noise, the on-channel repeater does not remove the output signal generated due to ambiguity.
Accordingly, an on-channel repeater is required for solving the above-mentioned drawbacks, that is, for allowing the output signal thereof to be the same as the output signal of the main transmitter, for allowing low time-delaying of the two output signals, for removing the noise and multi-path signals generated due to the transmission channel between the main transmitter and the on-channel repeater so that the on-channel repeater has a. superior characteristic of the output signal to that of the input signal, and for removing the feedback signal generated due to the low isolation of the transmission/reception antennas so that the transmission output power of the on-channel repeater can be increased.